1. Field of the Invention
The present invention generally relates to a current detection circuit, and more particularly to a current detection circuit and a protection circuit for converting input current into voltage with a current/voltage converting element, comparing the converted voltage with a reference voltage, and outputting an output signal in accordance with the magnitude relation obtained from the comparison.
2. Description of the Related Art
A rechargeable accumulator battery such as a lithium ion battery has its characteristic deteriorated by overcharging and/or over-discharging. Accordingly, a protection circuit is provided to a battery pack using an accumulator battery for protecting the accumulator battery from overcharging and/or over-discharging.
The protection circuit detects current flowing between the accumulator battery and a load or a charger, and detects an overcharging state or an over-discharging state based on the detection result. The protection circuit turns off a switching element provided between the accumulator battery and the load or the charger. By turning off the switching element with the protection circuit, the accumulator battery can be protected by being separated from the load or the charger. Here, a current detection circuit is provided to the protection circuit for detecting the overcharging state and/or the over-discharging state.
FIG. 8 is a block diagram showing a configuration of a conventional current detection circuit.
A current detection circuit 100 includes a sense resistance Rs and a comparator circuit 101. The sense resistance Rs is connected in series between a terminal Tin1 and a terminal Tin2 through which detection current flows. A junction point between one end of the sense resistance Rs and the terminal Tin1 is connected to an input terminal Tin11 of the comparator circuit 101, and a junction point between the other end of the sense resistance Rs and the terminal Tin2 is connected to an input terminal Tin12 of the comparator circuit 101.
The comparator circuit 101 includes a reference voltage generation circuit 111 and a comparator 112. The reference voltage generation circuit 111 generates a reference voltage Vref. The reference voltage Vref generated in the reference voltage generation circuit 111 is applied to an inverting input terminal of the comparator 112.
A base potential side of the reference voltage generation circuit 111 has the input terminal Tin12 connected thereto that is applied with the potential of the other end of the sense resistance Rs. A noninverting input terminal of the comparator 112 has the input terminal Tin11 connected thereto and is thus connected to the one end of the sense resistance Rs.
The comparator 112 compares a detection voltage Vs generated, in accordance with detection current, in the sense resistance Rs and the reference voltage Vref generated in the reference voltage generation circuit 111. The comparator 112 provides a high level output when the detection voltage Vs is greater than the reference voltage Vref and provides a low level output when the detection voltage Vs is less than the reference voltage Vref. The output of the comparator 112 is connected to an output terminal Tsout. The output terminal Tsout is supplied to a control circuit of the protection circuit. When the output from the output terminal Tsout of the current detection circuit 100 is a high level output, that is, when an overcharging state is detected, the control circuit switches off a switching element connected in series to the accumulator battery and eliminates the overcharging state (see Japanese Laid-Open Patent Application No. 6-188641).
However, with the conventional current detection circuit, current detection is executed according to a constant reference voltage Vref without considering the temperature characteristic of the voltage Vs converted by the sense resistance Rs. This leads to a problem where detection current varies depending on temperature.